Now if I'm not allowed a question on pancakes in body and soul section, u wont be allowed to get away with slabs. :-) unless you can give a good reason why this is in the right section :-) lol
Some tend to be a bit skimpy on thickness, (like B&Q's), which means they're not too strong and can crack rather easily. But if you have a carefully laid strong supporting bed, then this isn't too much of a problem. They might be a bit slippery in the wet to start with, but should weather to a slight roughness in time.
If they are to be laid over an existing concrete surface, any thickness can be used. otherwise don't try it unless they are "" AT LEAST """!!!! three cm thick. Thinner will certainly crack.